Miniature unidirectional condenser microphones require high quality and very small acoustical resistance elements having predictable resistance characteristics. Resistance elements of porous materials are potentially advantageous from standpoints of performance, cost and ease of assembly. However, potentially useful porous elements, if manufactured in thin sheets to provide the dimensional requirements suitable for a miniaturized microphone, tend to be characterized by a non-uniform porosity per unit area. The production of multiple acoustical resistance elements of miniature size and predictably uniform acoustical resistance characteristics is thus not possible. That is, since an acoustical resistance of said materials varies across the surface of the materials, a relatively large area is required to establish a predictable acoustical resistance; if acoustical resistance elements of sizes required for miniature microphones are fabricated from such materials, the individual small elements vary in their acoustical resistance. Thus, when incorporated into microphones, they impart diverse performance characteristics.